Meridional Section Research Articles

A coupled steady thermo-electromagnetic problem in axisymmetric geometries. Mathematical and numerical analysis

Abstract This paper focuses on the analysis of a steady thermo-electromagnetic problem related to the modeling of induction heating processes. Taking advantage of the cylindrical symmetry, the original three-dimensional problem can be reduced to a two-dimensional one on a meridional section, provided that the current density has only the azimuthal component. A variational formulation is presented in appropriately weighted Sobolev spaces, and the existence of a solution is established by employing a fixed-point argument. Furthermore, uniqueness and additional regularity results are proved under reasonable assumptions on the physical coefficients. A finite element approximation combined with a fixed-point iteration scheme is proposed for the numerical solution of the problem. A priori error estimates are obtained to quantify the accuracy of the approximation. Finally, numerical results are reported to validate the theoretical estimates and assess the performance of the method in a physical application.

Revisiting circulation and water masses over the East Antarctic margin (80–150°E)

Full-depth hydrographic sections of the BROKE experiment in 1996 (across the Antarctic margin from 80 to 150°E; Bindoff et al., 2000) were revisited for the first time during the 2018/2019 austral summer. We describe the subsurface physical oceanography in 2019 and the hydrographic changes between 1996 and 2019 not documented in earlier studies. The survey captured decadal changes in ocean structure from the southern flank of the Antarctic Circumpolar Current (ACC) to the continental shelves. In five cross-slope meridional sections, where 1996 and 2019 measurements are comparable (112, 120, 128, 140, and 150°E), the poleward shift of the southern boundary of the ACC (50–120 km) prevailed near the continental rise. The simultaneous displacement of barotropic ACC fronts and poleward migration of deep water contributed to full-depth warming (0.1–1.6 °C) and potentially to a reduction in the bottom water volume. Freshening was widely observed from the deep to bottom layers (∼0.02 g/kg), with the signal extending from the upper continental slope. Bottom-intensified freshening was accompanied by an oxygenation of 10–20 μmol/kg, indicating that freshening-driven oxygenation of bottom layers counteracted the deoxygenation effect of the poleward barotropic frontal shift. Westward transport of the Antarctic Slope Current decreased by more than 10 Sv from 1996 to 2019 in the five cross-slope sections; its frontal features and current axis shifted offshore by more than 20 km in 112–140°E. Additionally, subsurface warming along modified Circumpolar Deep Water by up to 0.4 °C was commonly detected across the upper continental slope. For the 2019 hydrography, shelf water sufficiently dense to form bottom water (>28.35 kg/m3) was found to the east of Mertz Polynya (142–148°E), implying a pathway for dense shelf water export from the eastern margin of Mertz Polynya. Our findings underscore the importance of sustained efforts for in-situ observations that widely cover the East Antarctic margin.

Numerical investigation on cavitation performance for centrifugal pumps with different impeller inlet geometry

In the centrifugal pump, cavitation often leads to the noise and pressure pulsation, further affects the performance and operation of the pump. Therefore, it is essential to improve cavitation performance at the stage of pump design. In this paper, three centrifugal pump impellers are designed by using different inlet geometry, where one is the conventional type and has cross section diffusion of flow passage along flow direction, and other two impellers are proposed and have cross section contraction of flow passage from impeller inlet to exit. For comparison of cavitation performance, the three-dimensional cavitating turbulent flows are simulated using the RANS method for the pumps. The results show that the pumps with the proposed meridional section have much better cavitation performance at design point while their hydraulic efficiency is also improved at larger flow rate, compared with that with the conventional meridional section design. Extending the blade leading edge of the proposed impeller is very helpful to obtain better cavitation performance further due to the uniform flow and smaller pressure drop around impeller inlet.

Seawater physics and chemistry along the Med-SHIP transects in the Mediterranean Sea in 2016

The Mediterranean Sea has been sampled irregularly by research vessels in the past, mostly by national expeditions in regional waters. To monitor the hydrographic, biogeochemical and circulation changes in the Mediterranean Sea, a systematic repeat oceanographic survey programme called Med-SHIP was recommended by the Mediterranean Science Commission (CIESM) in 2011, as part of the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP). Med-SHIP consists of zonal and meridional surveys with different frequencies, where comprehensive physical and biogeochemical properties are measured with the highest international standards. The first zonal survey was done in 2011 and repeated in 2018. In addition, a network of meridional (and other key) hydrographic sections were designed: the first cycle of these sections was completed in 2016, with three cruises funded by the EU project EUROFLEETS2. This paper presents the physical and chemical data of the meridional and key transects in the Western and Eastern Mediterranean Sea collected during those cruises.

Stratification of Indonesian Throughflow Water and Its Circulation along 125E in the Banggai - Maluku Sea

secondary pathway of Indonesian Throughflow (ITF) that enters from its inflow portal of the northern Maluku Sea is assumed to recirculate in the Banggai - Maluku Sea, where its upper-layer circulation returns into the Pacific and deeper flows continue southward into Seram/Banda Sea via Lifamatola Strait. However, direct observation in this key region is still limited. Here, using direct CTD (Conductivity Temperature Depth) casts and shipboard ADCP (Acoustic Doppler Curent Profiler) measurement datasets from BUDEE (Banggai Upwelling Dynamics and Ecosystem Experiment) cruise in September 2023, we study stratification and structure of ITF water and its circulation in a meridional section along 125E. The results show the water mass stratification of the mixed layer having a depth of 0-75m with a temperature range of 26-29°C, while the thermocline layer has a depth of 28-407m with a temperature range of 23-26°C, and the deep layer has a depth of 407-1000m with a temperature value of 4-12°C. The current pattern of the Banggai Sea Maluku Sea at a depth of 52-400m is more dominantly influenced by non-tidal currents, the influence of tidal currents only covers a depth of 52m less than non-tidal currents.

GOBAI-O2: temporally and spatially resolved fields of ocean interior dissolved oxygen over nearly 2 decades

Abstract. For about 2 decades, oceanographers have been installing oxygen sensors on Argo profiling floats to be deployed throughout the world ocean, with the stated objective of better constraining trends and variability in the ocean's inventory of oxygen. Until now, measurements from these Argo-float-mounted oxygen sensors have been mainly used for localized process studies on air–sea oxygen exchange, upper-ocean primary production, biological pump efficiency, and oxygen minimum zone dynamics. Here, we present a new four-dimensional gridded product of ocean interior oxygen, derived via machine learning algorithms trained on dissolved oxygen observations from Argo-float-mounted sensors and discrete measurements from ship-based surveys and applied to temperature and salinity fields constructed from the global Argo array. The data product is called GOBAI-O2, which stands for Gridded Ocean Biogeochemistry from Artificial Intelligence – Oxygen (Sharp et al., 2022; https://doi.org/10.25921/z72m-yz67); it covers 86 % of the global ocean area on a 1∘ × 1∘ (latitude × longitude) grid, spans the years 2004–2022 with a monthly resolution, and extends from the ocean surface to a depth of 2 km on 58 levels. Two types of machine learning algorithms – random forest regressions and feed-forward neural networks – are used in the development of GOBAI-O2, and the performance of those algorithms is assessed using real observations and simulated observations from Earth system model output. Machine learning represents a relatively new method for gap filling ocean interior biogeochemical observations and should be explored along with statistical and interpolation-based techniques. GOBAI-O2 is evaluated through comparisons to the oxygen climatology from the World Ocean Atlas, the mapped oxygen product from the Global Ocean Data Analysis Project and to direct observations from large-scale hydrographic research cruises. Finally, potential uses for GOBAI-O2 are demonstrated by presenting average oxygen fields on isobaric and isopycnal surfaces, average oxygen fields across vertical–meridional sections, climatological seasonal cycles of oxygen averaged over different pressure layers, and globally integrated time series of oxygen. GOBAI-O2 indicates a declining trend in the oxygen inventory in the upper 2 km of the global ocean of 0.79 ± 0.04 % per decade between 2004 and 2022.

Zonal circulation in the North Atlantic ocean at 52°W from WOCE-WHP and CLIVAR sections: 1997, 2003 and 2012

The A20 line is a meridional hydrographic section located at 52°W that cuts through the western North Atlantic Subtropical Gyre (NASG). It encloses the main paths of the Atlantic Meridional Overturning Circulation (AMOC). Using data from three A20 hydrographic cruises carried out in 1997, 2003 and 2012 together with Acoustic Doppler Current Profiler data and the velocities from an inverse box model, the circulation of the western NASG is estimated. The Gulf Stream is the main poleward path of the AMOC, carrying 155.3 ± 11.1, 102.7 ± 13.5 and 181.1 ± 14.9 Sv in 1997, 2003 and 2012, respectively (1 Sv = 106 m3/s ∼ 109 kg/s). In opposite direction, the Deep Western Boundary Current crosses the section at the northern/southern boundaries with a mass transport of −21.2 ± 8.9/29.0 ± 9.1, −14.4 ± 10.8/14.2 ± 8.1 and −37.9 ± 10.2/44.5 ± 9.8 Sv in 1997, 2003 and 2012, respectively. A net heat exchange from the ocean to the atmosphere is estimated to be −0.7 ± 0.1 PW and −0.6 ± 0.1 PW in 1997 and 2012, respectively, but is negligible in 2003 (0.1 ± 0.1 PW). The freshwater flux is significantly lower in 2003 (0.3 ± 0.1 Sv) than in 1997 (0.6 ± 0.1 Sv) and 2012 (0.6 ± 0.1 Sv). Ocean numerical models such as ECCO, GLORYS and MOM are used to address the interannual variability between the three surveys, but only the GLORYS output roughly agrees with the hydrographic data. GLORYS suggests a heat transport from the ocean to the atmosphere throughout the year and a net freshwater flux supported by precipitation plus river runoff higher than evaporation in all seasons except the spring.

Isotopes illustrate vertical transport of anthropogenic Pb by reversible scavenging within Pacific Ocean particle veils

Reversible scavenging, the oceanographic process by which dissolved metals exchange onto and off sinking particles and are thereby transported to deeper depths, has been well established for the metal thorium for decades. Reversible scavenging both deepens the elemental distribution of adsorptive elements and shortens their oceanic residence times in the ocean compared to nonadsorptive metals, and scavenging ultimately removes elements from the ocean via sedimentation. Thus, it is important to understand which metals undergo reversible scavenging and under what conditions. Recently, reversible scavenging has been invoked in global biogeochemical models of a range of metals including lead, iron, copper, and zinc to fit modeled data to observations of oceanic dissolved metal distributions. Nonetheless, the effects of reversible scavenging remain difficult to visualize in ocean sections of dissolved metals and to distinguish from other processes such as biological regeneration. Here, we show that particle-rich "veils" descending from high-productivity zones in the equatorial and North Pacific provide idealized illustrations of reversible scavenging of dissolved lead (Pb). A meridional section of dissolved Pb isotope ratios across the central Pacific shows that where particle concentrations are sufficiently high, such as within particle veils, vertical transport of anthropogenic surface-dissolved Pb isotope ratios toward the deep ocean is manifested as columnar isotope anomalies. Modeling of this effect shows that reversible scavenging within particle-rich waters allows anthropogenic Pb isotope ratios from the surface to penetrate ancient deep waters on timescales sufficiently rapid to overcome horizontal mixing of deep water Pb isotope ratios along abyssal isopycnals.

A North Pacific Meridional Section (U.S. GEOTRACES GP15) of Helium Isotopes and Noble Gases I: Deep Water Distributions

AbstractThe noble gas signature of incoming Pacific Bottom Water (PBW), when compared to North Atlantic Deep Water, indicates the addition of 450 ± 70 GT a−1glacial melt water to form AABW and subsequently PBW. The downstream evolution of this signature between the southern (20°S to equator) and northern (25°–45°N) bottom waters indicates a decrease in sea level pressure around Antarctica over the past two millennia. Vertical profiles of noble gases in the deep Pacific show exponential relationships with depth with scale heights identical to temperature and salinity. Unlike the other noble gases, helium isotopes show evidence of mid‐depth injection of non‐atmospheric helium. Using observed deviations from exponential behavior, we quantify its magnitude and isotope ratio. There is a clear latitude trend in the isotope ratio of this added helium that decreases from a high exceeding 9 RA(atmospheric3He/4He ratio) in the south to around 8 RAnear the equator. North of 30–40°N, it systematically decreases northward to a low of ∼2 RAnorth of 50°N. This decline results from a combination of northward decline in seafloor spreading, release of radiogenic helium from increased sediment thickness, and the possible emission of radiogenic helium through cold seeps along the Alaskan and North American margins. Finally, we derive an improved method of computing the excess helium isotope concentrations and that the distributions of bottom water3HeXS/4HeXSare consistent with what is known about bottom water flow patterns and the input of low3He/4He sedimentary helium.

Climatological Features of the Vento Norte Phenomenon in the Extreme South of Brazil

Downslope windstorm known as Vento Norte (VNOR; Portuguese for “North Wind”) is a common phenomenon that occurs in southern Brazil during the winter season. Hence, this study attempted to investigate the climatological characteristics of VNOR using seventeen years (2004–2020) of hourly observations collected at seven meteorological stations distributed over the central region of Rio Grande do Sul State. The VNOR windstorm episodes are identified by intense wind gusts and warm air advection from the northern direction. They were selected from the data set obtained during the winter in the city of Santa Maria (SM). Statistical analysis showed that the detected VNOR events were characterized by mean wind gusts ≈15 m.s-1, mean wind direction of 350° and mean air temperature of 27 °C. Average duration of the events was about 9 h, with the longest event lasting 21 h. Characteristics and effects of this phenomenon were compared with those in other locations (meridional and zonal sections). Average values of wind gusts from the northern direction presented a significant increase of ≈200% for the winter period in SM. Nonetheless, a less significant increase in wind gusts was recorded in the meridional (28%) and zonal (41%) sections away from SM. The central location of SM has favorable topographic characteristics for this amplification, with a sharp altitude difference caused by the plateau- plain interface of ≈300 m. Our findings showed that the VNOR phenomenon mainly affects the climate of the southern region of Brazil, with a local amplification in the city of SM.

A Glider View of the Spreading and Mixing Processes of Antarctic Intermediate Water in the Northeastern Subtropical Atlantic

The Antarctic Intermediate Water (AAIW), one of the most important global intermediate water masses, spreads over the world ocean. Its propagation limit at the Northeast Subtropical Atlantic is characterized by its encounter with the Mediterranean Water (MW), which presents dissimilar thermohaline properties. Previous studies of the AAIW in this region have been based on traditional oceanographic cruise observations, which were later complemented by observations using autonomous systems such as ARGO floats. However, these observations present limitations for the study of processes occurring at mesoscale and smaller scales. In this study, we used high-resolution observations made by cutting edge platforms such as underwater gliders. Specifically, a meridional glider section realized in spring 2016 between the islands of Madeira and Gran Canaria has been used. The temperature, salinity and dissolved oxygen minima have allowed the detection of the AAIW signal north of the Canarian archipelago and significantly westward from its main northward propagation pathway in this region. The results of this work have shown that the encounter of AAIW and MW generates thermohaline intrusions or interleaving layers. It is suggested that double diffusion processes may play a role in the development of these structures, which may be important for water masses mixing and, therefore, in determining the northward spreading boundary of AAIW. The use of the high-resolution glider observations combined with other data products is essential for the study of water masses and dynamics when relevant processes have a wide range of scales.

What Controls the Partition between the Cold and Warm Routes in the Meridional Overturning Circulation?

Abstract The origins of the upper limb of the Atlantic meridional overturning circulation and the partition among different routes has been quantified with models at eddy-permitting and one eddy-resolving model or with low-resolution models assimilating observations. Here, a step toward bridging this gap is taken by using the Southern Ocean State Estimate (SOSE) at the eddy-permitting 1/6° horizontal resolution to compute Lagrangian diagnostics from virtual particle trajectories advected between 6.7°S and two meridional sections: one at Drake Passage (cold route) and the other from South Africa to Antarctica (warm route). Our results agree with the prevailing concept attributing the largest transport contribution to the warm route with 12.3 Sv (88%) (1 Sv ≡ 106 m3 s−1) compared with 1.7 Sv (12%) for the cold route. These results are compared with a similar Lagrangian experiment performed with the lower-resolution state estimate from Estimating the Circulation and Climate of the Ocean. Eulerian and Lagrangian means highlight an overall increase in the transport of the major South Atlantic currents with finer resolution, resulting in a relatively larger contribution from the cold route. In particular, the Malvinas Current to Antarctic Circumpolar Current (MC/ACC) ratio plays a more important role on the routes partition than the increased Agulhas Leakage. The relative influence of the mean flow versus the eddy flow on the routes partition is investigated by computing the mean and eddy kinetic energies and the Lagrangian-based eddy diffusivity. Lagrangian diffusivity estimates are largest in the Agulhas and Malvinas regions but advection by the mean flow dominates everywhere.

NUMERICAL AND EXPERIMENTAL ANALYSIS OF A CENTRIFUGAL PUMP WITH DIFFERENT ROTOR GEOMETRIES

The paper presents a comparative analysis of the operation of two variants of centrifugal pump rotors, a description of the main parameters, and the influence of the blade geometry on the performance characteristics obtained. Rotors have been designed using the arc and point method. Based on the developed 3D CAD models, the rotors were printed using the rapid prototyping method on a 3D printer in FFF (Fused Filament Fabrication) technology, in order to experimentally verify the performance, by placing them on the Armfield FM50 test stand. The analysis part of the CFD includes a fluid flow in Ansys Fluent. The process of creating a flow domain and generating a structural mesh was described, along with the definition of boundary conditions, the definition of physical conditions and the turbulence model. The distribution of pressures and velocities in the meridional sections is shown graphically. The chapter with the experimental analysis contains a description of the measuring stand and the methodology used. The results obtained made it possible to generate the characteristics, making it possible to compare the results received. The results allowed to note the influence of geometry on the behavior of the rotors during operation in the system and to indicate that the arc rotor gets a 7% higher head and 2% higher efficiency than the point method rotor, which gives the basis for its commercial use in industry.

Marine Heatwaves, Upwelling, and Atmospheric Conditions during the Monsoon Period at the Northern Coast of the Gulf of Guinea

Ocean conditions influence the economies and climate of West Africa. Based on the 30-year daily Optimum Interpolation Sea Surface Temperature (OISST) dataset during May–October, upwelling surface variability and marine heatwaves (MHWs) at the northern coast of the Gulf of Guinea are investigated. The cooling surface decreases more rapidly around Cape Palmas than around Cape Three Points and extends eastward. MHWs variability exhibits a frequent occurrence of such events since 2015 that is consistent with the observed oceanic warming and the decrease in upwelling surface. The empirical orthogonal functions performed on the annual cumulated intensity of MHWs show four variability modes that include the whole northern coast, an east–west dipole between the two capes, a contrast between the northern coast at the two capes and the meridional section east of 5° E, and a north–south opposition. These patterns show 3-year, 6-year, and 8-year trends, and are related to coastal upwelling at the northern coast of the Gulf of Guinea. Similarly, surface ocean and atmospheric conditions are modified according to MHW periods. These changes take place before, during, and after MHW events. These results could be used to understand how this change influences the marine ecosystem, the local fisheries resources, and the extreme rainfall episodes in West Africa.

Distributions of aluminum, manganese, cobalt, and lead in the western South Pacific: Interplay between the South and North Pacific

Aluminum (Al), manganese (Mn), cobalt (Co), and lead (Pb) are strongly scavenged from seawater. We reported that each element is uniquely related to ocean circulation in the North Pacific (Zheng et al., 2019). Herein, we present the full-depth distributions of these elements in the western South Pacific, which include meridional sections along 170°W (GEOTRACES GP19). We determined dissolved (d) and total dissolvable (td) concentrations using filtered and unfiltered seawater without UV treatment, and we calculated labile particulate (lp) concentrations as the difference between td and d concentrations. This and the previous studies present the basin scale distributions, which enable us to investigate first order processes that drive the biogeochemistry of Al, Mn, Co, and Pb in the Pacific Ocean. The meridional section of dAl along 170°W (GP19)-160°W (GPc06) from 64°S to 54°N indicates that elevated concentrations (maximum 6.1 nmol/kg) occur between 40°S and 10°S from surface to bottom. However, the maxima of lpAl occur at high latitudes. The lpAl/tdAl ratio has a minimum of 0.26 ± 0.12 (ave ± sd, n = 116) in the zone from 30°S to 0°S. Based on these results, we propose a hypothesis that weathering on land has a significant effect on the distribution of Al in the ocean. Intensive weathering on tropical and subtropical islands and Australia forms kaolinite-dominated soils and laterite. This process provides dAl and kaolinite to the ocean. The supply of kaolinite results in kaolinite-dominated sediments that become a major bottom source for dAl. In contrast, strong sources of Mn and Co are continental shelves around the northern boundary. Dissolved Mn and dCo are released from sediments by manganese reduction and carried by intermediate water circulation. In particular, dCo spreads in the North Pacific Intermediate Water (NPIW), Equatorial Pacific Intermediate Water (EqPIW), and Antarctic Intermediate Water (AAIW); 23–59 pmol/kg at a potential density anomaly (σθ) of 27.0. This is partly owing to the uptake of dCo by phytoplankton and remineralization from settling particles. The dPb concentrations are 10 ± 6 pmol/kg (n = 397) in the South Pacific and 30 ± 20 pmol/kg (n = 566) in the North Pacific. The distribution of dPb is characterized by a maximum in the Subtropical Mode Water (SMW) and Central Mode Water (CMW) with σθ∼26 in the North Pacific. These results indicate that Pb is predominantly supplied by anthropogenic aerosols from Asia and Russia to the Pacific Ocean. Because Pb is not actively taken up by phytoplankton, Pb enters mode waters during winter convection and is transported with mode waters.

Regulation of the Respiration Quotient Across Ocean Basins

AbstractA key uncertainty for predicting future ocean oxygen levels is the response and feedback of organic matter respiration demand. One poorly constrained component of the respiration demand is the oxygen‐to‐carbon remineralization ratio—the respiration quotient. Currently, multiple biological hypotheses can explain variation in the respiration quotient of organic matter produced in the surface ocean. To test these hypotheses, we directly quantified the particulate respiration quotient in 715 samples along a meridional section of the Atlantic Ocean and compared to previous Pacific Ocean observations. We demonstrate significant regional shifts in the respiration quotient and a two‐basin average of 1.16. Possible diel oscillations were also observed in the respiration quotient. Basin and regional variation in the respiration quotient were positively linked to temperature, N versus P stress, and plankton size structure. These observations suggest a complex regulation of the respiration quotient with important implications for the regional coupling of carbon and oxygen cycling.

Performance Enhancement of a Centrifugal Compressor by Designing a Tandem Cascade Diffuser

The performance of a vane diffuser plays an important role in transforming the high kinetic energy into pressure energy at the impeller outlet of a centrifugal compressor. In this study, the performance enhancement of a centrifugal compressor is achieved by designing a tandem cascade diffuser. An optimum value of the total bending angle of a tandem cascade diffuser is obtained through numerical simulation. The total bending angle is defined as the angle between the tangent line of the front blade arc line at the leading edge point and the tangent line of the rear blade arc line at the trailing edge point. The range of the total bending angle increases from zero to 21°. The simulation results show that the variation of the total bending angle has a great impact on the performances of the compressor stage. The best performance is achieved by the 10° model, by which the minimum total pressure loss coefficient and the maximum static pressure recovery coefficient are obtained. The mechanism of performance improvement by choosing a reasonable total bending angle is that the separated flow zone in the diffuser is constrained and the distribution of radial velocity at the inlet and outlet of the diffuser is more uniformed. With the 10° model, the separated zone almost completely disappears in the diffuser and a distribution of more uniform radial velocity along the meridional section is obtained. Compared with the stage of the prototype with a single row of vane diffuser, the stage with the newly designed tandem vane diffuser (10° model) achieved performance improvement, the efficiency increased about 6%, and the total pressure ratio increased about 3.5% at the flow coefficient of 0.15.

INVASIVE SPECIES OF DIATOMS IN THE AUTUMN PHYTOPLANKTON OF THE CASPIAN SEA: THE ROLE IN THE FORMATION OF TOTAL BIOMASS AND DISTRIBUTION IN THE SALINITY GRADIENT

The phytoplankton structure in ecologically diverse areas of the sea and the role of marine invasive species in the formation of the community were studied on the meridional and latitudinal trans-Caspian sections in the autumn period of 2008, 2009, and 2012. It was established that the transformation of the phytoplankton community continues in the Caspian Sea, associated with the entry of the Black Sea diatoms Chaetoceros peruvianus, Cerataulina pelagica, and Pseudo-nitzschia seriata into their composition. During the autumn bloom of phytoplankton in November 2008, the number of invasive species reached 1.3-2.3 × 10 cells/L, C. peruvianus and P. seriata to the total weight biomass of the community reached 49-50%. The highest abundance of invasive species was recorded in the shelf areas of the Middle Caspian Sea in its eastern ( C. peruvianus , 2.3 × 10 cells/L), western ( P. seriata , 1.4 × 10 cells/L), and northern ( C. pelagica , 1.3 × 10 cells/L) parts. The north boundary of the distribution of these species in the Caspian Sea was the 5.0 isohaline, which coincided with the highly productive frontal zone (4.0-6.0) of the marginal filter of the Volga River. For the first time, it was shown that the C. peruvianus diatom was a part of the phytoplankton of the upper productive 25-30-meter water layer both in the Middle and in the Southern Caspian during the periods preceding the autumn bloom of phytoplankton (September-October). During that time the most considerable abundance of this species (1.6 × 10cells/L) was recorded in the shallow areas on the Apsheron Sill and the eastern part of the Middle Caspian in the zone of coastal wind upwelling.

DETERMINATION OF KINEMATIC CHARACTERISTICS OF METAL PLASTIC FLOW UNDER CONDITIONS OF AXIAL SYMMETRY OF THE DEFORMATION PROCESS

With axisymmetric deformation, the deformable body and the load have a common axis of symmetry. Such deformation occurs in numerous technological operations. About 70% of parts obtained by cold extrusion are deformed under conditions of axial symmetry. The plane problem of the theory of plasticity is reduced to a solution in the framework of a two-dimensional statement, when the motion of points in the section of a workpiece is analyzed. Each point can move only in the section plane, and its velocity can be decomposed into two mutually perpendicular directions along the coordinate axes. For plane deformation, it is assumed that the velocity in the direction of the third coordinate axis is equal to zero. The presence of axial symmetry allows us to confine ourselves to studying the behavior of points located on the plane of the meridional section of the workpiece. In this case, each point can move only in the section plane and its velocity can be decomposed into two orthogonal directions: along the axis and along the radius. The component of the velocity vector in the circumferential direction is equal to zero, so only four of the six independent components of the strain rate tensor remain. In this regard, axisymmetric problems of the theory of plasticity are of considerable interest from the point of view of solving applied problems. The article discusses the possibility of using mixed Euler and Lagrange coordinates to determine the components of the strain rate tensor in plastic deformation processes characterized by the axisymmetric nature of metal plastic flow. The vector field of displacements at each point in space reflects the transformation of the initial (non-deformed) configuration into the current one, and therefore determines the configuration of the deformed body in space in a certain frame of reference. The deformation process is first considered in a single Cartesian coordinate system, and then in a cylindrical coordinate system, the use of which is more appropriate for axisymmetric deformation. It is assumed that the functions of the Euler coordinates from the Lagrange coordinates are obtained by approximating the experimental data.

Алгоритм маршового розрахунку надзвукового обтікання ракети з відхиля-ємою носовою частиною

This paper presents a marching algorithm for the calculation of supersonic flow past a tilting-nose rocket. A feature of the algorithm is that the marching direction of supersonic flow calculation for the nose does not coincide with that for the main part of the rocket surface. Because of this, at first flow past the nose is calculated in a cylindrical coordinate system, the flow field parameters being stored at marching cross-sections. The start and the end of the parameter storage interval in the flow field are determined from the condition of the intersection of the bow shock wave with a plane in which an initial flow field is to be specified for the calculation of flow past the main part of the rocket surface. The flow field is interpolated in two stages, First, in the cylindrical coordinate system bound to the main part of the rocket surface in the initial data plane, the radial coordinates of the bow shock wave are determined at meridional sections. From the radial coordinates of points on the rocket surface and the bow shock wave, new computational grid node coordinates are determined at meridional sections in the cylindrical coordinate system of the main part. Using the new computational grid coordinates specified in the cylindrical coordinate system of the main part, old coordinates specified in the cylindrical coordinate system of the nose are determined with the use of expressions that relate the two coordinate systems to each other. The flow parameters at a point with the calculated coordinates are calculated using linear interpolation of the stored flow field parameters in the cylindrical coordinate system bound to the nose. The calculated flow field is used as initial data for the marching calculation of the main part of the rocket, The paper presents the results of calculation of the aerodynamic characteristics of a tilting-nose rocket in a supersonic flow at different values of the nose angle. The proposed algorithm may be used in a prompt calculation of the aerodynamic characteristics of rockets with tilting elements. In doing so, use may be made of a standard program of rocket flow calculation with an added block for the storage and interpolation of the flow field in a tilted cylindrical coordinate system with a shifted origin, which allows the marching direction to be changed.